The separation of the centerline gear on take-off was the result of a combination of an over-pressure condition in the strut and a gland nut that was weakened by a manufacturing defect. When the aircraft was serviced in Vancouver, nine days prior to the accident, the maintenance crew followed the procedures depicted on the instruction plate on the gear leg. The information on the plate was exemplified in such a way as to invite a reversal in the order of charging for the system. Reversing the order results in an overcharged gear strut. Once the initial charging procedures were completed, there was little possibility that an overcharge would be discovered during routine monitoring inspections as the Daily Gas Pressure Monitoring check only insured that the gear strut pressures were above minimum values. There was nothing in the check to alert ground maintenance workers to an overcharged condition that was still well below the red line on the gauge. The following Engineering Branch reports were completed: LP 136/97 FDR/CVR Analysis LP 141/97 Gland Nut Examination LP 142/97 Centerline Landing GearAnalysis The separation of the centerline gear on take-off was the result of a combination of an over-pressure condition in the strut and a gland nut that was weakened by a manufacturing defect. When the aircraft was serviced in Vancouver, nine days prior to the accident, the maintenance crew followed the procedures depicted on the instruction plate on the gear leg. The information on the plate was exemplified in such a way as to invite a reversal in the order of charging for the system. Reversing the order results in an overcharged gear strut. Once the initial charging procedures were completed, there was little possibility that an overcharge would be discovered during routine monitoring inspections as the Daily Gas Pressure Monitoring check only insured that the gear strut pressures were above minimum values. There was nothing in the check to alert ground maintenance workers to an overcharged condition that was still well below the red line on the gauge. The following Engineering Branch reports were completed: LP 136/97 FDR/CVR Analysis LP 141/97 Gland Nut Examination LP 142/97 Centerline Landing Gear The shock strut assembly of the centerline landing gear had a Stage 1 static pressure that was considerably higher than it should have been. The placarded instructions for servicing the gear's shock strut were exemplified in such a way as to invite a reversal in the order of charging of its low-and high-pressure stages. A reversal in the order of charging of the shock strut stages results in a very stiff, overcharged condition for the gear. Instructions for recharging of the centerline gear in the aircraft maintenance manual (AMM) at TASK 12-14-32-614-806 dated Jul 01/97 need clarification. The Daily Gas Pressure Monitoring check was unlikely to alert service technicians to an overcharged condition. The strength of the gland nut was reduced as a result of a manufacturing defect.Findings The shock strut assembly of the centerline landing gear had a Stage 1 static pressure that was considerably higher than it should have been. The placarded instructions for servicing the gear's shock strut were exemplified in such a way as to invite a reversal in the order of charging of its low-and high-pressure stages. A reversal in the order of charging of the shock strut stages results in a very stiff, overcharged condition for the gear. Instructions for recharging of the centerline gear in the aircraft maintenance manual (AMM) at TASK 12-14-32-614-806 dated Jul 01/97 need clarification. The Daily Gas Pressure Monitoring check was unlikely to alert service technicians to an overcharged condition. The strength of the gland nut was reduced as a result of a manufacturing defect. The centerline gear separated from the aircraft on take-off when the weakened gland nut was forced out by excessive gas pressure. Contributing factors to the occurrence were as follows: the placarded servicing instructions for the shock strut contained an error in the example, which led to overcharging of the strut system; the existing Daily Gas Pressure Monitoring check was inadequate to alert service technicians to the overcharging of the strut; the scaling of the low-pressure gauge was such that its red line and its needle position would not arouse suspicion when the strut was overcharged; and the gland nut was weakened by a manufacturing defect.Causes and Contributing Factors The centerline gear separated from the aircraft on take-off when the weakened gland nut was forced out by excessive gas pressure. Contributing factors to the occurrence were as follows: the placarded servicing instructions for the shock strut contained an error in the example, which led to overcharging of the strut system; the existing Daily Gas Pressure Monitoring check was inadequate to alert service technicians to the overcharging of the strut; the scaling of the low-pressure gauge was such that its red line and its needle position would not arouse suspicion when the strut was overcharged; and the gland nut was weakened by a manufacturing defect. All stocks of centerline landing gear gland nuts were checked by Messier-Dowty for correctness of thread profile. All 59 gland nuts installed on aircraft were inspected. One more mis-machined nut was found with the same incorrect thread profile as that of C-FYLD. The thread profiles of all gland nuts are now being 100 percent inspected at Messier-Dowty and at the manufacturing subcontractor by additional methods that will expose any faulty thread profile. All Aircraft Maintenance Manual procedures on CLG servicing have been revised to improve their clarity; they are available in the 01 July 1998 AMM revision. The Daily Gas Pressure Monitoring Check procedure was modified in order to add a check for over-pressure and to make it clearer; the TR was available 15 June 1998. Modifications to the gauges and placards have been produced and were incorporated in Messier-Dowty production units as of February 1999. A modification to make the gland nut of steel instead of aluminium has been produced and incorporated in Messier-Dowty's April 1999 production.Safety Action All stocks of centerline landing gear gland nuts were checked by Messier-Dowty for correctness of thread profile. All 59 gland nuts installed on aircraft were inspected. One more mis-machined nut was found with the same incorrect thread profile as that of C-FYLD. The thread profiles of all gland nuts are now being 100 percent inspected at Messier-Dowty and at the manufacturing subcontractor by additional methods that will expose any faulty thread profile. All Aircraft Maintenance Manual procedures on CLG servicing have been revised to improve their clarity; they are available in the 01 July 1998 AMM revision. The Daily Gas Pressure Monitoring Check procedure was modified in order to add a check for over-pressure and to make it clearer; the TR was available 15 June 1998. Modifications to the gauges and placards have been produced and were incorporated in Messier-Dowty production units as of February 1999. A modification to make the gland nut of steel instead of aluminium has been produced and incorporated in Messier-Dowty's April 1999 production.